This invention relates to products which thicken or gel liquid nitroalkanes. More particularly, this invention relates to nitrate esters of galactomannan gums.
The use of polysaccharide gums as thickening agents for aqueous systems is well known. Galactomannan gums have been used extensively as thickeners and gelling agents for food products, paints, and explosive systems. Chemically, galactomannan gums are high molecular weight polysaccharides comprising mannose and galactose units bonded together through ether linkages. The molecules are generally considered to be composed of long straight chains of mannose units having side branches of galactose units. Galactomannan gums, which include guar gum and locust bean gum, are natural colloids obtained from the endosperms of leguminous seeds, such as guar, locust bean, honey locust, etc.
Although galactomannan gums have been effective thickeners for aqueous systems, they have not generally been found effective as thickeners or gelling agents for non-aqueous systems. In particular, such gums do not thicken liquid nitroalkanes. Liquid nitroalkanes, particularly nitromethane, are well known for their utility in propellants and explosives. Such propellants and explosives are advantageously thickened or gelled before use. Thickening serves several purposes including providing a better product when filled into elastic casings, providing homogeneous systems when solid ingredients such as hollow glass microspheres or ammonium nitrate prills are present, preventing leaks when contained by enclosures having small perforations, and reducing rates of evaporation of liquids from the systems.
Compounds which have been used to thicken or gel liquid nitroalkane-containing explosives include cyanoethyl ethers of galactomannan gums, nitrate esters of cellulose, and high molecular weight polyoxygethylene. Cyanoethyl ethers of galactomannan gums are described by Nordgren, Robert, U.S. Pat. No. 3,755,292 issued Aug. 28, 1973 and Jordan, W. A., U.S. Pat. No. 3,666,577 issued May 30, 1972. High molecular wieght polyoxyethylene as a thickener for liquid nitroalkanes is the subject of Jones, L. R., U.S. Pat. No. 3,318,741 issued May 9, 1967, incorporated herein by reference.
Cellulose and starch are polysaccharides which have been nitrated. Nitrated starch is used primarily as an explosive or as a thickener for aqueous systems, but it has not been found effective as a thickener for non-aqueous systems. Nitrated cellulose thickens liquid nitroalkanes; however, relatively large amounts are required to form explosive slurries. Nitrated cellulose and nitrated starch are usually prepared by reacting the respective polysaccharide with a nitrating acid. The nitrating acid is generally a mixed acid which contains a major porportion of sulfuric acid, nitric acid, and water. The nitrated products are usually purified by repeated treatments with boiling water.